> I've been told that material 43 ferrites are good for general HF RFI
> issues. However, I've also been told that material 77 is best below 5 MHz
> and material 43 is best 7 MHz and up (within the HF spectrum).
We really shouldn't select materials based on such loose generalities.
43 material has lower impedance per turn, but the Q reaches unity at very
high frequencies. It is good for "high stress" HF applications, where Q must
be high and loss controlled.
77 material has a Q of 1 below 160 meters. That means it behaves mostly like
a resistance above lower HF. It also has less impedance than a material like
43 up high in frequency.
We really need to understand what the core must do in a specific
application, and not just pick a core based on some "frequency range" that
only applies to one specific application.
73 is probably good for RFI filters all over HF. 43 for RFI filters at VHF.
For HF transmitting baluns:
61 or 65 for baluns with high power.
43 for extreme power
73 for very low power or receive applications
I'd never use a 43 material for RFI suppression except at VHF.
73 Tom
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